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Pneumonia is an infection of the gas exchange segments of the lung parenchyma. It can cause a profound inflammatory response leading to airspace accumulation of puru-lent debris. Pneumonia costs are $8 billion annually, accounts for nearly one-tenth of all hospital admissions, and remains a leading cause of mortality in the United States.

Etiology and Risk Factors

• There are numerous risk factors as discussed in (Table 3D.1).

• The pathogens involved vary depending upon the host (see Table 3D.2).

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Diagnosis

• Pneumonia is sometimes divided into two categories depending upon the causative agent and presentation (see Table 3D.3). Note that considerable overlap exists be-tween the two categories and differentiation in the ED may be difficult.

• Patients typically complain of dyspnea, cough, and fever. Depending upon the etiol-ogy, they may also have night sweats, weight loss, myalgias, and localized extrapulmonary symptoms. History should focus on acuity symptom onset, presence of associated symptoms, recent travel history, immunization history, and comorbidities. In certain populations such as the elderly, pneumonia can present with nonspecific symptoms such as weakness and fatigue.

• Physical exam findings depend upon the etiology and the extent of lung involvement.

Pulmonary exam often reveals rales and decreased or bronchial breath sounds. Al-though sometimes difficult to assess in the ED, patients can also have dullness to percussion, tactile fremitus, and egophony. Associated findings include tachypnea, ta-chycardia, diaphoresis, AMS, and increased work of breathing. Note that the pulmo-nary examination sometimes does not correlate with CXR findings.

• Laboratory Studies

• Sputum—Because of the low sensitivity of the sputum Gram stains, the clinical utility in the ED is controversial. This test is most helpful if a single predominant organism is identified and requires an adequate specimen (>25 WBCs and <10 epithelial cells Table 3D.1. Risk factors for pneumonia

Risk Factor Comments

Aspiration/absent gag reflex Stroke, intubation, seizure, altered mental status, sedative use

Mucociliary clearance disorders Smoking, alcohol, COPD, cystic fibrosis, chronic bronchitis, viral infections

Alteration of normal oral flora Acute illness and antibiotic use

Immunocompromise AIDS*, diabetes, transplant, steroid use, asplenia, sickle cell disease, uremia, neoplasia, chemotherapy, extremes of age, complement deficiency

Hematogeonous Indwelling catheters, intrathoracic devices Geography/environment American southwest (Valley Fever), Ohio/

MississippiValleys (histoplasmosis, blastomycosis), Southeast Asia (tuberculosis), pigeon droppings (psittacosis), bovinesources (Q fever), buildings with contaminated water supply

Community dwelling Dormitory, prison, barracks, nursing home

* AIDS: acquired immune deficiency syndrome

Table 3D.2. Common pathogens in pneumonia Population Causative Pathogen

Community acquired Streptococcus pneumoniae, Mycoplasma pneumoniae, viruses, Chlamydia pneumoniae, Haemophilus influenzae, Legionella, Staphylococcus aureus

Nosocomial (>likely Gram-negative bacilli, Staphylococcus aureus, anaerobes, to be resistant to and Streptococcus pneumoniae (less frequent)

antibacterial therapy)

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per high power field) as well as experienced laboratory personnel. Sputum cultures are helpful for critically ill or immunocompromised patients but are rarely of use to the EP and should not be routinely ordered. An acid fast (AFB) stain is indicated patients with risk factors or presentation consistent with tuberculosis (TB).

• Serum

• There are no specific laboratories for pneumonia although CBC, electrolytes, and renal function studies are often ordered. These tests should be obtained routinely in patients who are critically ill or if significant comorbid disease is present. Note that presence of an elevated WBC does not identify a bacterial source. Nor does a normal WBC rule it out.

• Serum antibody titers are available for Legionella, Mycoplasma pneumoniae, and viruses among others but are of little use in the ED.

• CXR

• Ordered in nearly all patients with suspected pneumonia although studies de-bate the utility of this study in otherwise healthy people being treated empiri-cally as an outpatient.

• Certain radiographic patterns have been described depending upon the etiology (see Table 3D.4). These patterns sometimes vary and do not provide an accurate means of diagnosis.

• Note that radiographic findings often lag behind clinical symptoms. Patients with early disease and immunosuppression may not have classic findings.

• Differential diagnosis includes COPD, bronchitis, asthma, allergic reaction, and PE among others.

Treatment

• Stabilization of cardiopulmonary status is the first priority. Depending on the disease severity, patients may have respiratory compromise and/or circulatory collapse that mandate immediate intervention.

• Early antibiotic treatment decreases morbidity and mortality. Empiric therapy should be started as soon as possible after appropriate resuscitative measures. Many patients are treated as outpatients, although certain groups are at risk for poor outcome and should be considered for hospital admission (see Table 3D.5). Admitted patients should Table 3D.3. Typical and atypical pneumonias

Category Pathogens Presentation

Typical Streptococcus pneumoniae Acute onset

(usually Haemophilus influenzae Shaking chills and high fever bacterial) Staphylococcus aureus Cough with purulent sputum

Klebsiella pneumoniae Dyspnea

Anaerobes Pleuritic chest pain

Psuedomonas aeruginosa

Atypical Mycoplasma pneumoniae Gradual onset

Viruses Low grade fever

Legionella Scant sputum

Chlamydia pneumoniae Mild respiratory complaints Mycobacterium tuberculosis Extrapulmonary complaints Pneumocystis carinii Mycoplasma: myalgias, headache,

sore throat, rash

Viral: upper respiratory symptoms Legionella: AMS, gastrointestinal symptoms

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receive IV antibiotics and outpatients appropriate oral therapy as indicated for their age, comorbid conditions, and suspected pathogen (see Table 3D.6).

• All discharged patients should follow-up with their primary care physician.

Suggested Reading

1. Feldman CF. Pneumonia in the elderly. Clin Chest Med 1999; 20(3):563.

2. Dean NC. Use of prognostic scoring and outcome assessment tools in the admission decision for community-acquired pneumonia. Clin Chest Med 1999; 20(3):521.

3. American Thoracic Society: Guidelines for the initial management of adults with com-munity acquired pneumonia: Diagnosis, assessment of severity, and initial microbial therapy. Am Rev Respir Dis 1999; 148:1418.

Table 3D.4. Radiographic presentation of pneumonia Radiographic Pattern Pathogens

Lobar Streptococcus pneumoniae

Klebsiella pneumoniae (classically RUL, bulging fissure)

Patchy Atypical agents

Haemophilus influenzae Staphylococcus aureus Fungi

Viruses

Interstitial Mycoplasma pneumoniae

Viruses

Pneumocystis carinii

Abscess Tuberculosis and other fungi

Staphylococcus aureus

Effusion Streptococcus pneumoniae

Staphylococcus aureus Mycoplasma pneumoniae Viruses

Tuberculosis

Apical Tuberculosis

Klebsiella pneumoniae

Table 3D.5. High risk patients

Risk Factor Comment

Abnormal vital signs Tachypnea (>30/min)

Hypotension (<70 mm Hg systolic) O₂ saturation <95% on room air Extremes of age <6 mos or >60 yr

Comorbid conditions or disease Pregnancy

Congestive heart failure Renal or hepatic insufficiency

Immunosuppression: HIV, asplenia, diabetes, alcohol/drug abuse

Recent hospital admission Patients who fail initial therapy

Risk of aspiration Stroke, AMS, alcohol abuse

Pathogen Suspected tuberculosis

Gram-negative bacilli on sputum examination Inability to care for self as outpatient

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4. Emergency Medicine Reports: Community-acquired pneumonia (CAP) in the geriatric patient: Evaluation, risk-stratification, and antimicrobial treatment guidelines for inpa-tient and outpainpa-tient management 2000; 21(20).

5. The Sanford Guide to Antimicrobial Therapy, 31st edition. 2001.